Electronic phenomena studied in the nordic countries

Frustrated square-lattice antiferromagnet Sr2CuTe0.5W0.5O6

Not scheduled

15m

Max IV Lund

Speaker

Mr Otto Mustonen (Aalto University)

Description

Square-lattice antiferromagnets can be described using a Heisenberg J1-J2 model with two interactions: nearest neighbor J1 (sides of the square) and next-nearest neighbor J2 (diagonal of the square). The classical ground states of the J1-J2 model are ferromagnetic order, Néel AFM order and columnar AFM order. Dominating antiferromagnetic J1 leads to Néel order and J2 to columnar order. Anderson [1] first proposed that by frustrating the Néel order in a S=1/2 square-lattice antiferromagnet a quantum spin liquid (QSL) state might emerge. This is expected to occur in the highly frustrated J2/J1 ≈ 0.5 region but has not been experimentally observed. Sr2CuTeO6 and Sr2CuWO6 are B-site ordered double perovskites with Cu2+ (S=1/2) on a square-lattice due to a Jahn-Teller distortion. Neutron scattering experiments [2,3] have shown the magnetic interactions to be highly two-dimensional in these compounds. The magnetic ordering is Néel type in Sr2CuTeO6 (J2/J1 = 0.03) and columnar in Sr2CuWO6 (J2/J1 = 7.92). This difference in exchange strengths is caused by differences in W-O and Te-O hybridization affecting the Cu-O-Cu super-exchange. We report on the magnetic properties of the solid solution Sr2CuTe0.5W0.5O6. The random distribution of tellurium and tungsten on the B’’-site leads to random exchange pathways between copper ions. A broad maximum is observed in the DC magnetic susceptibility in Sr2CuTeO6 at Tmax = 73 K and in Sr2CuWO6 at Tmax = 83 K. In Sr2CuTe0.5W0.5O6 this maximum is shifts to 50 K suggesting increased frustration. Heat capacity measuremends reveal a significant low-temperature electronic contribution to heat capacity in Sr2CuTe0.5W0.5O6 but not in the end members despite all three compounds being insulators. This suggest Sr2CuTe0.5W0.5O6 might be a QSL candidate. [1] P.W. ANDERSON, Science, 235, 1196 (1987). [2] P. Babkevich, V.M. Katukuri, B. Fåk, S. Rols, T. Fennell, D. Pajić, H. Tanaka, T. Pardini, R.R.P. Singh, A. Mitrushchenkov, O.V. Yazyev, and H.M. Rønnow, Phys. Rev. Lett. 117, 237203 (2016). [3] H.C. Walker, O. Mustonen, S. Vasala, D.J. Voneshen, M.D. Le, D.T. Adroja, and M. Karppinen, Phys. Rev. B 94, 64411 (2016).